1. Field of the Invention
The present invention relates to a light guide, and particularly to a communication system using a sheet-shaped light guide which includes particles for scattering light in a sheet-shaped optical medium and propagates light incident from one end face of the light guide to the other end face side thereof while scattering the light by means of the particles.
2. Description of the Related Art
Heretofore, as described in, for example, U.S. Pat. Nos. 5,548,670 and 5,542,017, a light guide which includes particles for scattering light in an optical medium, such as PMMA (poly-methyl methacrylate), and which propagates light incident from one end face thereof to the other end face side thereof while scattering the light by means of the particles, is known.
Such a light guide propagates light by using the effect of total reflection at the interface between the side face of the light guide and a surrounding medium (air or cladding layer) while repeatedly scattering the light by means of the particles in the optical medium. Accordingly, when compared to a light guide which propagates light only by using the effect of total reflection, such a light guide has an advantage that it is possible to allow light, the intensity distribution of which is made even, to be emitted from an exit end face. As for this kind of a light guide, as described in, for example, U.S. Pat. No. 5,822,475, by utilizing such an advantage, it is conceived to apply the light guide in order to constitute an optical data bus (sheet bus). The optical data bus is formed by use of a sheet-shaped optical medium. One input part for inputting optical signals is coupled to one end face of the sheet-shaped optical medium, and a plurality of output parts are coupled to the other end face thereof. Therefore, the optical data bus distributes an inputted optical signal as a common signal to the plurality of output parts.
Moreover, as an optical data bus of this type, as described in, for example, Japanese Unexamined Patent Publication No. 11(1999)-031035, that in which light diffusion portions are provided on a light-incident-side end portion of the sheet-shaped optical medium so as to correspond to respective signal light incident portions, and the signal light, which is diffused and branched by the light diffusion portions, is propagated toward a light-exit-side end portion of the optical medium, is also known.
A communication system using a sheet-shaped light guide, which includes particles for scattering light in a sheet-shaped optical medium as described in U.S. Pat. No. 5,822,475, may be installed in various apparatuses. For this purpose, the sheet-shaped light guide must be bent in many cases. However, the sheet-shaped light guide generally has a certain thickness, and is not highly flexible. Therefore, when the space in the apparatus is narrow or has an intricate shape, in some cases, it is impossible to dispose the bent sheet-shaped light guide within the apparatuses. This can be a serious problem when the electrically wired communication system in various apparatuses is replaced by a communication system using the sheet-shaped light guide.
Additionally, such a sheet-shaped light guide as described above is often used by connecting the light guide to optical fibers. However, when a sheet-shaped light guide which has a relatively large thickness to fit the outer diameters of the optical fibers is applied thereto, the above problem becomes more serious because the sheet-shaped light guide becomes particularly hard to bend.